2,835 research outputs found
The perturbed sublimation rim of the dust disk around the post-AGB binary IRAS08544-4431
Context: Post-Asymptotic Giant Branch (AGB) binaries are surrounded by stable
dusty and gaseous disks similar to the ones around young stellar objects.
Whereas significant effort is spent on modeling observations of disks around
young stellar objects, the disks around post-AGB binaries receive significantly
less attention, even though they pose significant constraints on theories of
disk physics and binary evolution. Aims: We want to examine the structure of
and phenomena at play in circumbinary disks around post-AGB stars. We continue
the analysis of our near-infrared interferometric image of the inner rim of the
circumbinary disk around IRAS08544-4431. We want to understand the physics
governing this inner disk rim. Methods: We use a radiative transfer model of a
dusty disk to reproduce simultaneously the photometry as well as the
near-infrared interferometric dataset on IRAS08544-4431. The model assumes
hydrostatic equilibrium and takes dust settling self-consistently into account.
Results: The best-fit radiative transfer model shows excellent agreement with
the spectral energy distribution up to mm wavelengths as well as with the
PIONIER visibility data. It requires a rounded inner rim structure, starting at
a radius of 8.25 au. However, the model does not fully reproduce the detected
over-resolved flux nor the azimuthal flux distribution of the inner rim. While
the asymmetric inner disk rim structure is likely to be the consequence of
disk-binary interactions, the origin of the additional over-resolved flux
remains unclear. Conclusions: As in young stellar objects, the disk inner rim
of IRAS08544-4431 is ruled by dust sublimation physics. Additional observations
are needed to understand the origin of the extended flux and the azimuthal
perturbation at the inner rim of the disk.Comment: Accepted for publication in A&A, 13 figures, 13 page
Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae
S-type AGB stars have a C/O ratio which suggests that they are transition
objects between oxygen-rich M-type stars and carbon-rich C-type stars. As such,
their circumstellar compositions of gas and dust are thought to be sensitive to
their precise C/O ratio, and it is therefore of particular interest to examine
their circumstellar properties.
We present new Herschel HIFI and PACS sub-millimetre and far-infrared line
observations of several molecular species towards the S-type AGB star W Aql. We
use these observations, which probe a wide range of gas temperatures, to
constrain the circumstellar properties of W Aql, including mass-loss rate and
molecular abundances. We used radiative transfer codes to model the
circumstellar dust and molecular line emission to determine circumstellar
properties and molecular abundances. We assumed a spherically symmetric
envelope formed by a constant mass-loss rate driven by an accelerating wind.
Our model includes fully integrated H2O line cooling as part of the solution of
the energy balance. We detect circumstellar molecular lines from CO, H2O, SiO,
HCN, and, for the first time in an S-type AGB star, NH3. The radiative transfer
calculations result in an estimated mass-loss rate for W Aql of 4.0e-6 Msol
yr-1 based on the 12CO lines. The estimated 12CO/13CO ratio is 29, which is in
line with ratios previously derived for S-type AGB stars. We find an H2O
abundance of 1.5e-5, which is intermediate to the abundances expected for M and
C stars, and an ortho/para ratio for H2O that is consistent with formation at
warm temperatures. We find an HCN abundance of 3e-6, and, although no CN lines
are detected using HIFI, we are able to put some constraints on the abundance,
6e-6, and distribution of CN in W Aql's circumstellar envelope using
ground-based data. We find an SiO abundance of 3e-6, and an NH3 abundance of
1.7e-5, confined to a small envelope.Comment: 17 pages, 15 figure
Proton radioactivity within a generalized liquid drop model
The proton radioactivity half-lives of spherical proton emitters are
investigated theoretically. The potential barriers preventing the emission of
protons are determined in the quasimolecular shape path within a generalized
liquid drop model (GLDM) including the proximity effects between nuclei in a
neck and the mass and charge asymmetry. The penetrability is calculated with
the WKB approximation. The spectroscopic factor has been taken into account in
half-life calculation, which is obtained by employing the relativistic mean
field (RMF) theory combined with the BCS method with the force NL3. The
half-lives within the GLDM are compared with the experimental data and other
theoretical values. The GLDM works quite well for spherical proton emitters
when the spectroscopic factors are considered, indicating the necessity of
introducing the spectroscopic factor and the success of the GLDM for proton
emission. Finally, we present two formulas for proton emission half-life
calculation similar to the Viola-Seaborg formulas and Royer's formulas of alpha
decay.Comment: 7 pages, 1 figur
On the liquid drop model mass formulas and decay of the heaviest nuclei
The coefficients of different macro-microscopic Liquid Drop Model mass formulas have been determined by a least square fitting procedure to 2027 experimental atomic masses. A rms deviation of 0.54 MeV can be reached. The remaining differences come mainly from the determination of the shell and pairing energies. Extrapolations are compared to 161 new experimental masses and to 656 mass evaluations. The different fits lead to a surface energy coefficient of around 17-18 MeV. Finally, decay potential barriers are revisited and predictions of decay half-lives of still unknown superheavy elements are given from previously proposed analytical formulas and from extrapolated Q values
High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates
Many important hominid-bearing fossil localities in East Africa are in regions that are extremely hot and dry. Although humans are well adapted to such conditions, it has been inferred that East African environments were cooler or more wooded during the Pliocene and Pleistocene when this region was a central stage of human evolution. Here we show that the Turkana Basin, Kenya—today one of the hottest places on Earth—has been continually hot during the past 4 million years. The distribution of ^(13)C-^(18)O bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 °C and often in excess of 35 °C. Similar soil temperatures are observed today in the Turkana Basin and reflect high air temperatures combined with solar heating of the soil surface. These results are specific to periods of soil carbonate formation, and we suggest that such periods composed a large fraction of integrated time in the Turkana Basin. If correct, this interpretation has implications for human thermophysiology and implies a long-standing human association with marginal environments
Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tuc
We aim to determine abundances of Li, O and Na in a sample of of 110 turn-off
(TO) stars, in order to study the evolution of light elements in this cluster
and to put our results in perspective with observations of other globular and
open clusters, as well as with field stars. We use medium resolution spectra
obtained with the GIRAFFE spectrograph at the ESO 8.2m Kueyen VLT telescope and
use state of the art 1D model atmospheres and NLTE line transfer to determine
the abundances. We also employ CO5BOLD hydrodynamical simulations to assess the
impact of stellar granulation on the line formation and inferred abundances.
Our results confirm the existence of Na-O abundance anti-correlation and hint
towards a possible Li-O anti-correlation in the TO stars of 47 Tuc. We find no
convincing evidence supporting the existence of Li-Na correlation. The obtained
3D NLTE mean lithium abundance in a sample of 94 TO stars where Li lines were
detected reliably,
dex, appears to be significantly lower than what is observed in other globular
clusters. At the same time, star-to-star spread in Li abundance is also larger
than seen in other clusters. The highest Li abundance observed in 47 Tuc is
about 0.1 dex lower than the lowest Li abundance observed among the un-depleted
stars of the metal-poor open cluster NGC 2243. The lithium abundances in 47
Tuc, when put into context with observations in other clusters and field stars,
suggest that stars that are more metal-rich than [FeH] \sim -1.0 experience
significant lithium depletion during their lifetime on the main sequence, while
the more metal-poor stars do not. Rather strikingly, our results suggest that
initial lithium abundance with which the star was created may only depend on
its age (the younger the star, the higher its Li content) and not on its
metallicity.Comment: 24 pages, 13 figures; discussion and conclusions expanded. Accepted
for publication in A&
Making On-Demand Routing Efficient with Route-Request Aggregation
In theory, on-demand routing is very attractive for mobile ad hoc networks
(MANET), because it induces signaling only for those destinations for which
there is data traffic. However, in practice, the signaling overhead of existing
on-demand routing protocols becomes excessive as the rate of topology changes
increases due to mobility or other causes. We introduce the first on-demand
routing approach that eliminates the main limitation of on-demand routing by
aggregating route requests (RREQ) for the same destinations. The approach can
be applied to any existing on-demand routing protocol, and we introduce the
Ad-hoc Demand-Aggregated Routing with Adaptation (ADARA) as an example of how
RREQ aggregation can be used. ADARA is compared to AODV and OLSR using
discrete-event simulations, and the results show that aggregating RREQs can
make on-demand routing more efficient than existing proactive or on-demand
routing protocols
Uncoupling of EGFR–RAS signaling and nuclear localization of YBX1 in colorectal cancer
The transcription factor YBX1 can act as a mediator of signals transmitted via
the EGFR–RAS–MAPK axis. YBX1 expression has been associated with tumor
progression and prognosis in multiple types of cancer. Immunohistochemical
studies have revealed dependency between YBX1 expression and individual EGFR
family members. We analyzed YBX1 and EGFR family proteins in a colorectal
cancer (CRC) cohort and provide functional analyses of YBX1 in the context of
EGFR–RAS–MAPK signaling. Immunohistochemistry for YBX1 and EGFR family
receptors with two antibodies for YBX1 and EGFR were performed and related to
clinicopathological data. We employed Caco2 cells expressing an inducible
KRASV12 gene to determine effects on localization and levels of YBX1. Mouse
xenografts of Caco2-KRASV12 cells were used to determine YBX1 dynamics in a
tissue context. The two different antibodies against YBX1 showed discordant
immunohistochemical stainings in cell culture and clinical specimens.
Expression of YBX1 and EGFR family members were not correlated in CRC.
Analysis of Caco2 xenografts displayed again heterogeneity of YBX1 staining
with both antibodies. Our results suggest that YBX1 is controlled via complex
regulatory mechanisms involving tumor stroma interaction and signal
transduction processes. Our study highlights that YBX1 antibodies have
different specificities, advocating their use in a combined manner
If It Walks Like Systematic Exclusion and Quacks Like Systematic Exclusion: Follow-Up on Removal of Women and African-Americans in Jury Selection in South Carolina Capital Cases, 1997-2014
This Article builds on an earlier study analyzing bases and rates of removal of women and African-American jurors in a set of South Carolina capital cases decided between 1997 and 2012. We examine and assess additional data from new perspectives in order to establish a more robust, statistically strengthened response to the original research question: whether, and if so, why, prospective women and African-American jurors were disproportionately removed in different stages of jury selection in a set of South Carolina capital cases.
The study and the article it builds on add to decades of empirical research exploring the impacts (or lack thereof) of Batson and related jurisprudence on jury selection practices. The findings from the earlier study persisted with the stronger dataset in this study and are consistent with many previous studies’ findings indicating that capital jury selection procedures serve to systematically siphon off women and African-Americans through the death-qualification process and peremptory strikes.
Key findings in the earlier study included that the prosecution struck 35% of strike-eligible black potential jurors, accounting for removing 15% of black venire members; that approximately 32% of black venire members were removed for opposition to the death penalty; and that the combined effects of these two stages prevented a total of 47% of black venire members from serving, compared to those stages preventing a combined 16% of the white venire pool from serving. Those findings have for the most part persisted with the stronger dataset here, with slight variations. Here, the prosecution struck 29% of strike-eligible black potential jurors (the average of a 33% strike rate for black men and 25% for black women), accounting for removing 13% of black venire members; approximately 24% of black venire members were removed for opposition to the death penalty; and the combined effects of these two stages prevented a total of 42% of black venire members from serving. This is compared to the prosecution striking 12.5% of strike-eligible white potential jurors, which equates to about 7% of the overall white venire pool; and 6.2% of white potential jurors being removed for anti-death views, with the two stages preventing, combined, an approximate 13% of white venire members from serving
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